Using a conventional clutch mechanism where a combustion engine is comprised in the drive system's power unit configuration, disconnecting the gearbox's input shaft from the combustion engine during a shifting process in the gearbox, entails disadvantages, such as heating of the clutch mechanism's plates, which results in an increased fuel consumption and wear of the clutch plates. There are also large losses as a result, in particular when the vehicle is started. A conventional clutch mechanism is also relatively heavy and costly. It also occupies a relatively large space in the vehicle. Friction losses also arise from the use of a hydraulic converter/torque converter commonly used in automatic transmissions. By ensuring that the vehicle has a drive system in which the output shaft of the combustion engine, the rotor of the electrical machine and the input shaft of the gearbox are connected with a planetary gear, the conventional clutch mechanism and the disadvantages associated therewith may be avoided. A vehicle with a drive system of this type constitutes prior art, as set out in EP 1 319 546 and SE 536 329.
Certainly, a range of advantageous methods to control a vehicle with a drive system of the type described in SE 536 329 constitute prior art, however there is naturally a constant endeavor to improve the manner of controlling such vehicles, especially in certain specific operating situations.